Contrive a secret plot or scheme, especially with selfish motives. For example, I think he has designs on my job, or Mary has designs on her sister's boyfriend. This term uses design in the sense of “a crafty plan,” a usage dating from about 1700.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.